When I first got my car, it was doing the same thing with the "more power at 3/4 throttle than on the floor" thing. Mine turned out to have a really dirty MAF.
One of my SHO friends had the same problem. To make sure the MAF was the culprit one of the other guys had us unplug it. We test drove it and it worked on that car, the power was back and it revved right out. We drove it back, cleaned the MAF and problem solved.
I have heard some say the unplugging the MAF thing as a test doesn't work, but it is worth a try, imho. 0$ and 1.5 minutes.
'94 Laser red 'vert. Still a 5-oh... for now